GB1581651A - Lubricating oil additive composition - Google Patents

Description

(54) LUBRICATING OIL ADDITIVE COMPOSITION (71) We, CHEVRON RESEARCH COMPANY, a corporation duly organised under the laws of the State of Delaware, United States of America, of 575 Market Street, San Francisco, California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to an antioxidant additive composition for a crankcase lubricating oil and to a lubricating oil composition containing said additive compo sition having improved antioxidation properties.

Hydrocarbon oils are partially oxidized when contacted with oxygen at elevated temperatures for long periods. The internal combustion engine is a model oxidator, since it contacts a hydrocarbon motor oil with air under agitation at high temperatures. Also, many of the metals (iron, copper, lead, nickel, etc.) used in the manufacture of the engine and in contact with both the oil and air, are effective oxidation catalysts which increase the rate of oxidation. The oxidation in motor oils is particularly acute in the modern internal combustion engine which is designed to operate under heavy work loads and at elevated temperatures.

The oxidation process produces acidic bodies within the motor oil which are corrosive to typical copper, lead, and cadmium engine bearings. It has also been discovered that the oxidation products contribute to piston ring sticking, the formation of sludges within the motor oil and an overall breakdown of viscosity characteristics of the lubricant.

Several effective oxidation inhibitors have been developed and are used in almost all of the conventional motor oils today. Typical of these inhibitors are the sulfurized oil-soluble organic compounds, such as wax sulfides and polysulfides, sulfurized olefins, sulfurized fatty acid esters, and sulfurized olefin esters, as well as zinc dithiophosphates and the oil-soluble phenolic and aromatic amine anti oxidants. These inhibitors, while exhibiting good antioxidant properties, are burdened by economic and oil contamination problems. It is preferred to maintain the sulfur content of the oil as low as possible, while at the same time receiving the benefits of the antioxidation property. A need, therefore, exists for an improved antioxidant that is stable at elevated temperatures, that can be employed in reduced concentrations, and that is economical and easy to produce.

U.S. Patent 2,718,501 discloses a synergistic mixture of a sulfur-containing compound, such as a wax sulfide or dioctadecyl disulfide, and an aroamtic amine compound having at least 2 aromatic rings, such as phenyl alpha-naphthyl amine, for use in preventing oxidation in lubricating oils.

U.S. Patent 2,729,691 disclosed a mixture of an arylamine antioxidant and a synergistic amount of an alkylenediamine for protecting organic material from oxidation.

U.S. Patent 2,958,663 discloses an extreme pressure lubricant composition containing from 0.01 to 5 percent each of sulfurized oleic acid, C18-C22 alkenyl succinic acid, chlorinated paraffin wax containing from 20 to 60 percent chlorine, diphenylamine and N,N-calicylal-1,2-propylenediamine.

U.S. Patent 3,345,292 disclosed stabilized alkyl substituted diaryl sulfides for use as functional fluids where the stabilizer can be diarylamine or alkylated phenol.

British Specification No. 757,219 discloses the use, as antioxidants, of di(hydroxyaryl) thioethers in conjunction with amines having a boiling point of at least 140"C in lubricating compositions based on dialkyl esters of aliphatic dicarboxylic acids suitable for use over a wide temperature range. The thioesters are substantially free from free sulfur and polysulfides.

It is an object of this invention to provide a synergistic additive composition having antioxidant properties in crankcases lubricating oil compositions.

According to one aspect of the invention, there is provided an antioxidant additive composition for a crankcase lubricating oil, the additive composition comprising in admixture (1) an oil-soluble antioxidant selected from sulfurized aromatic and alkylsulfides and polysulfides, sulfurized olefins, sulfurized carboxylic' acid esters and sulfurized ester-olefins, and (2) a primary amine of the formula

wherein each R is independently alkyl or alkenyl of at least 6 carbon atoms, R4 is alkylene of at least 2 carbon atoms, each A is independently hydrogen or C1-C18 alkyl, Het is a carbon chain forming with the N atom a 5- or 6-membered heterocyclic ring, optionally containing in place of one carbon atom an additional N or O hetero atom, x is an integer from 2 to 4, and y is an integer from 1 to 4.

According to another aspect of the invention there is provided a lubricating oil composition comprising an oil or lubricating viscosity and an antioxidant additive composition as described above.

It has been found that the defined antioxidants in combination with the defined amines complement each other in a synergistic manner, resulting in a combination having antioxidant properties superior to either additive alone. The amine component alone has virtually no antioxidant effect. However, when the defined codmbination of amine and antioxidant is added to a lubricating oil, less of the antioxidant is needed to obtain oxidation control than when the amine is not present.

Preferably, from 2 to 40 millimols of an oil-soluble zinc salt is present er kilogram of the lubricating oil composition. While this zinc salt is not required to achieve the synergistic effect from the combination of the antioxidant and the amine, an improved lubricating oil composition results from the use of all three additive components.

The compositions of this invention are highly stable additives for crankcase lubricating oils and impart excellent antioxidant properties to these oils.

In a preferred embodiment of the lubricating oil composition, 0.25 to 10 weight percent of the antioxidant is present and 0.001 to 5 weight percent of the amine is present. The weight ratio of the antioxidant to amine is ordinarily in the range of 1 to 0.001-21.

More preferably, 0.25 to about 2 weight percent of the antioxidant is present in the lubricating oil. More preferably, the amine is present in the amount of 0.01 to 0.3, preferably 0.05 to 0.3 weight percent.

In a further preferred embodiment, from 9 to 30 mmols per kilogram of the oilsoluble zinc salt is present.

The class of antioxidants which may be used are conventional sulfurcontaining antioxidants selected from sulfurized aromatic and alkyl sulfides and polysulfides, e.g. sulfurized wax sulfides or polysulfides, sulfurized olefins, sulfurized carboxylic acid esters and sulfurized ester-olefins.

The sulfurized fatty acid esters are prepared by reacting sulfur, sulfur monochloride, and/or sulfur dichloride with an unsaturated fatty ester under elevated temperatures. Typical esters include C1-C20 alkyl esters of C8-C24 unsaturated fatty acids, usch as palmitoleic, oleic, ricinoleic, petroselinic, vaccenic, linoleic, linolenic, oleostearic, licanic, paranaric, tariric, gadoleic, arachidonic and cetoleic.

Particularly good results have been obtained with mixed unsaturated fatty acid esters, such as are obtained from animal fats and vegetable oils, such as tall oil, linseed oil, olive oil, castor oil, peanut oil, rape oil, fish oil and sperm oil.

Exemplary fatty esters include lauryl tallate, methyl oleate, ethyl oleate, lauryl oleate, cetyl oleate, cetyl linoleate, lauryl ricinoleate, oleyl linoleate, olayl stearate, and alkyl glycerides.

Cross-sulfurized ester olefins, such as a sulfurized mixture of C10-C25 olefins with fatty acid esters of C10-C25 fatty acids and C1-C25 alkyl or alkenyl alcohols, wherein the fatty acid and/or the alcohol is unsaturated may also be used.

Sulfurized olefins which may be used as an antioxidant in the practice of this invention are prepared by the reaction of the C3-C8 olefin or a low-molecularweight polyolefin derived therefrom with a sulfur-containing compound such as sulfur, sulfur monochloride, and/or sulfur dichloride.

Another class of organic sulfur-containing compound which may be used is sulfurized aliphatic esters of an olefinic mono- or dicarboxylic acid, for example aliphatic alcohols of 1--30 carbon atoms, used to esterify monocarboxylic acids such as acrylic acid, methacrylic acid and 2,4-pentadienoic acid or fumaric acid, maleic acid and muconic acid. Sulfurization is carried out by recating these esters with elemental sulfur, sulfur monochloride and/or sulfur dichloride.

The preferred antioxidants are the sulfurized aromatic and alkyl sulfides, such as sulfurized dibenzylsulfide, dixylyl sulfide, dicetyl sulfide, diparaffin wax sulfide and polysulfide, and cracked wax-olefin sulfides. Particularly preferred are the sulfurized derivatives of the paraffin wax thiomers described in U.S Patent 2,346,156.

All of the sulfides and polysulfides included within the scope of this invention are sulfurized sulfides and polysulfides. That is, the sulfide or polysulfide has been reacted with additional sulfur, sulfur monochloride or sulfur dichloride after the initial formation of the sulfide. Residual chlorine that may be present in the antioxidant after sulfurization is not detrimental and may be beneficial.

The second component of the additive composition for use in lubricating oils is a primary amine.

The primary amines which can be used are those compounds defined by the following formulas:

wherein each A is independently hydrogen or C1-C18 alkyl, R is alkyl or alkenyl of at least 6 carbon atoms, R4 is an alkylene of at least 2 carbon atoms, x is an integer from 2 to 4, y is an integer from 1 to 4, and Het is a carbon chain forming with the N atom a 5- or 6-membered heterocyclic ring optionally containing in place of one carbon atom an additional N or 0 hetero atom.

Preferably A is hydrogen, x is 2 and R contains at least 12 carbon atoms. Also, in the polyamine compounds, it is preferred that the R group have from about 30 to about 250, preferably 30 to 120, carbon atoms. R as polyisobutylene is particularly preferred for the polyamine compounds.

When R is alkenyl, the alkenyl portion preferably has 1 to 2 olefinically unsaturated linkages per molecule. If a totally saturated group, is desired, the compound containing, e.g. a polyisobutylene group, can be hydrogenated with hydrogen over a noble metal catalyst, such as platinum, using conventional hydrogenation techniques.

The R group may be either branched or unbranched hydrocarbon. In the monoamine compounds, R is preferably alkyl of 12 to 22 carbon atoms, and more preferably is octadecyl.

The heterocyclic primary amines included within the invention have 5- or 6membered heterocyclic rings containing at least one nitrogen atom and optionally an additional nitrogen or oxygen hetero atom. The heterocyclic ring designated

can be saturated or unsaturated and is preferably piperazinyl, piperidinyl, imidazolyl, morpholinyl, pyrazolyl or pyridyl. The heterocyclic ring may be substituted by one or more alkyl groups which do not affect the synergistic activity of the amine.

The compounds included within the scope of the above formula are compounds whose methods of preparation are well known.

The zinc salts which may be used in this invention are oil-soluble zinc salts.

They are used in the lubricating oil to supply from 9 to 40 mmols of zinc per - kilogram of oil.

The zinc salt is preferably a zinc dihydrocarbyldithiophosphate having from 4 to 20 carbon atoms in each hydrocarbyl group. The zinc dihydrocarbyldithiophosphate is'formed by reacting the corresponding dihydrocarbyldithiophosphoric acid with a zinc base, such as zinc oxide, zinc hydroxide and zinc carbonate. The hydrocarbyl portions may be all aromatic, all aliphatic, or mixtures thereof.

Exemplary zinc dihydrocarbyldithiophosphates include: zinc di(n-octyl)dithophosphate, zinc butyl isooctyl dithiophosphate, zinc di(4-methyl-2-pentyl)dithiophosphate, zinc di(tetrapropenylphenyl)dithiophosphate, zinc di(2-ethyl-1-hexyl)dithiophosphate zinc di(isooctyl)dithiophosphate, zinc di(hexyl)dithiophosphate, zinc di(ethylphenyl)dithiophosphate, zinc di(amyl)dithiophosphate, zinc di(alkylphenyl)dithiophosphate, zinc hutylphenyldithiophosphate, and zinc di(octadecyl)dithiophosphate.

Preferred compounds are those zinc dihydrocarbyldithiophosphates having from 4 to 18 carbon atoms in each hydrocarbon group. Especially preferred are the zinc dialkyldithiophosphates wherein each alkyl group typically contains from 4 to 8 carbon atoms and the zinc di(alkylaryl)dithiophosphates wherein each alkylaryl group contains from 15 dto 21 carbon atoms.

The lubricating oil composition of the invention may conveniently be prepared by admixing, by conventional mixing techniques, the desired amount of antioxidant and amine in a suitable lubricating oil. The selection of the particular base oil and amine, as well as the amounts and ratios of each, depends upon the contemplated application of the lubricant and the presence of other additives.

Generally, however, the amount of oil-soluble antioxidant employed in the lubricating oil will vary from 0.25 to 10, and usually from 0.25 to 2, weight percent.

The primary amine will range from 0.01 to 2, and usually from 0.01 to 0.3, preferably from 0.05 to 0.3, weight percent based on the weight of the final composition. The weight ratio of organic oil-soluble antioxidant to amine will generally vary from 5-20 to 1, and usually from 1020 to 1.

Concentrates of the new additive composition of this invention can be prepared for easier handling and storage of the additive. Usually the concentrate will be 10 to 90% by weight additive composition and from 10 to 90% by weight lubricating oil diluent. Preferably the additiveocomposition comprises 20 to 80% by weight of the lubricating oil additive concentrate. This concentrate is diluted with additional oil before use.

The lubricating oil which may be used includes a wide variety of hydrocarbon oils such as naphthenic base, paraffin base, and mixed base oils. Other oils include lubricating oils derived from coal products and synthetic oils, e.g. alkylene polymers (such as propylene and butylene and mixtures thereof), alkylene oxidetype polymers (e.g. alkylene oxide polymers prepared by polymerizing alkylene oxides, such as ethylene oxide and propylene oxide, in the presence of water or alcohol, e.g. ethyl alcohol), carboxylic acid esters (e.g. those which are prepared by esterifying carboxylic acids, such as adipic acid, azelaic acid, suberic acid, sebacic acid, alkenylsuccinic acid, fumaric acid and maleic acid, with an alcohol such as butyl alcohol, hexyl alcohol, 2-ethylhexyl alcohol or pentaerythritol, liquid esters of phosphorus-containing acids such as trialkyl phosphate and tricresyl phosphate, alkylbenzenes, polyphenyls (e.g. biphenyls and terphenyls), alkylbiphenyl ethers, esters and polymers of silicon, e.g. tetraethyl silicate, tetraisopropyl silicate, hexa (4-methyl-2-pentyl) disilicate, poly(methyl)siloxane, and poly(methylphenylsiloxane). The lubricating oils may be used individually or in combinations whenever miscible, or whenever made so by use of mutual solents. The lubricating oils generally have a viscosity which ranges from 50 to 5000 SUS (Saybolt Universal Seconds), and usually from 100 to 1500 SUS at 100 F.

In addition to the antioxidant, the amine compound and the oil-soluble zinc salt, other additives may be used in the lubricating composition without affecting its high stability and performance over a wide temperature scale. One type of additive which may be used is a rust inhibitor. The rust inhibitor is used in many types of lubricants to suppress the formation of rust on the surface of metallic parts.

Typical rust inhibitors include sodium nitrite, alkenylsuccinic acid and derivatives thereof, alkylthioacetic acid and derivatives thereof, polyglycols and derivatives thereof, and alkoxylated amines and derivatives thereof. Other types of lubricating additives which may be use are metallic or ashless dispersants and detergents.

Typical of these are the conventional succinimides, succinates hydrocarbylalkylene polyamines, alkaline earth metal salts of alkylaryl sulfonates and phenates.

Other types of lubricating oil additives which may be used include antifoam agents (e.g. silicones, organic copolymers), stabilisers and antistain agents, tackiness agents, antichatter agents, dropping point improvers and antisquark agents, lubricant color correctors, extreme-pressure agents, oder control agents, detergents, antiwear agents and thickeners.

The presence of the amine in the lubricant composition increases the antioxidation properties of the oil-soluble, sulfur-containing antioxidant. With this combination, less of the antioxidant is necessary in the lubricant to achieve the desired antioxidation properties. If the antioxidant is used at conventional levels, increased oxidation protection is obtained.

The following Example is presented to illustrate the practice of specific embodiments of this invention.

EXAMPLE The combination of the amines with this antioxidant in improving the antioxidation properties of a lubricating oil over the use of either of the components individually is illustrated by the following test. The oxidation test uses the resistance of the test sample to oxidation using pure oxygen with a Dornte-type oxygen absorption apparatus (R. W. Dornte, "Oxidation of White Oils", Industrial and Engineering Chemistry, Vol. 28, page 26, 1936). The conditions are an atmosphere of pure oxygen exposed to the test oil maintained at a temperature of 340"F. The time required for 100 g of test sample to adsorb 1000 ml of oxygen is observed and reported in the following Table I. The test oil in section A is Midcontinent neutral oil containing 6% of a conventional succinimide dispersant, 0.05% terephthalic acid, 0.4% of a conventional rust inhibitor, and 9 mmols/kg of a zinc dithiophosphate. The test oil in sections B, C and D is a refined mineral oil.

TABLE I Oxidation Antioxidant 0.1% Primary Amine Life/Hrs.

5.2 A) 1% sulfurized diparaffin polysulfide 6.4 0.56 1% sulfurized diparaffin polysulfide dodecylamine 8.6 " 2-ethylhexylamine 8.0 Primene (Trade Mark) KMT' 7.1 Duomeen (Trade Mark) T2 7.5 oleyl-NH(CH2)3NH2 6.6 TABLE I (continued) Oxidation Antioxidant 0.1% Primary Amine Life/Hrs.

1% sulfurized diparaffin polysulfide PB,2EDA3 6.9 PB24EDA4 0.66 1% sulfurized diparaffin polysulfide PB24EDA4 9.8 " PB32EDA5 8.0 - N-(2-aminoethyl)piperazine 5.2 1% sulfurized diparaffin polysulfide ,, 10.1 - bis(aminopropyl)ethylene diamine 4.8 1% sulfurized diparaffin polysulfide ,, 10.4 B) 50 mmols/kg sulfurized diparaffin polysulfide (18.0% S) - 3.18 10 10 mmol/kg octadecylamine 15.75 " (15.09% S) - 4.80 10 10 mmols/kg octadecylamine 17.77 50 mmols-kg sulfurized ester (9.88% S) 2.33 10 10 mmols/kg octadecylamine 5.17 " (14.5% S) 1.03 10 10 mmols/kg octadecylamine 4.80 C) 50 mmols/kg sulfurized diparaffin polysulfide 5 2.5 mmols/kg octadecylamine 11 10 10 " ,, 18 " 20 " " 18 50 50 ,, ,, 21 TABLE I (Continued) Oxidation Antioxidant 0.1% Primary Amine Life/Hrs.

D) 32.5 mmols/kg sulfurized diparaffin polysulfide - 0.9 " 2,5 mmols/kg octadecylamine 1.3 10 10 ,, 9.5 " 20 ,, ,, 3.0 " 50 " " 9.5 25 " 0 " 2,5 mmols/kg octadecylamine 0 " 10 " " 0.8 " 50 " " 1.3

where the R group has approximately 18 carbon atoms 2C18H37NH(CH2)3NH2 3Reaction product of ethylene diamine (EDA) and polyisobutenyl chloride having a number average molecular weight of 530.

4Reaction product of EDA and polyisobutenyl chloride having a number average molecular weight of 950.

5Reaction product of EDA and polyisobutenyl chloride having a number average molecular weight of 1400.

6Base oil contains no zinc dithiophosphate.

Claims (11)

WHAT WE CLAIM IS:

1. An antioxidant additive composition for a crankcase lubricating oil, the additive composition comprising in admixture: (1) an oil-soluble antioxidant selected from sulfurized aromatic and alkyl sulfides and polysulfides, sulfurized olefins, sulfurized carboxylic acid esters, and sulfurized ester-olefins, and (2) a primary amine represented by the general formula:

wherein each R is independently alkyl or alkenyl of at least 6 carbon atoms, R4 is alkylene of at least 2 carbon atoms, each A is independently hydrogen or C1-C18 alkyl, Het is a carbon chain forming with the N atom a 5- or 6-membered heterocyclic ring, optionally containing in place of one carbon atom an additional N or O hetero atom, x is an integer from 2 to 4, and y is an integer from 1 to 4.

2. An additive composition as claimed in Claim 1, wherein the amine is a primary amine of the general formula:

in which R is alkyl of at least 12 carbon atoms, A is: hydrogen, and x is 2.

3. An additive composition as claimed in Claim 1, wherein the amine is octadecylamine or N-(2-aminoethyl)-piperazine.

4. An additive composition as claimed in any preceding claim, wherein the antioxidant is a sulfurized wax sulfide or polysulfide.

5. An additive composition as claimed in any preceding claim, wherein the weight ratio of said antioxidant to said amine is 1:0.001-21.

6. A lubricating oil composition comprising an oil of lubricating viscosity and an additive composition as claimed in any one of Claims 1 to 5.

7. An additive composition as claimed in Claim 6, wherein from 0.25 to 10 weight percent of the antioxidant and from 0.001 to 5 weight percent of the amine are present in the composition.

8. A composition as claimed in Claim 6 or 7, and further comprising an oil- sbluble zinc salt, said salt being present in an amount of from 2 to 40 millimols of the zinc salt per kilogram of composition.

9. A composition as claimed in Claim 8, wherein the zinc salt is a zinc dihydrocarbyldithiophosphate.

10. A lubricating oil composition in accordance with Claim 6, substantially as described in the foregoing Example.

11. A concentrate for a lubricating oil composition as claimed in Claim 6, comprising from 10 to 90% by weight of the additive composition and from 90 to 10% by weight of the oil of lubricating viscosity.